Does the sun influence climate? In today’s post we would like to introduce new studies from Spain and Portugal that shed light on this. In February 2017 a tree-ring study appeared in Climate of the Past. It was authored by Ernesto Tejedor et al, who made a temperature reconstruction for the Iberian Peninsula for the past 400 years.

The authors emphasize that the temperature fluctuations fit very well with the fluctuations in solar activity.

Warm phases coincide with periods of high solar activity. In total the region of study warmed up almost 3°C over the past 400 years, which reflects the transition from the Little Ice Age to the modern warm period — see figure below. However there were phases around 1625 and 1800 when temperatures were at today’s levels for a short time.

Temperature curve in the mountain regions of northern Spain over the past 400 years, compared to solar activity. Source: Tejedor et al. 2017.

Temperature variability in the Iberian Range since 1602 inferred from tree-ring records
Tree rings are an important proxy to understand the natural drivers of climate variability in the Mediterranean Basin and hence to improve future climate scenarios in a vulnerable region. Here, we compile 316 tree-ring width series from 11 conifer sites in the western Iberian Range. We apply a new standardization method based on the trunk basal area instead of the tree cambial age to develop a regional chronology which preserves high- to low-frequency variability. A new reconstruction for the 1602–2012 period correlates at −0.78 with observational September temperatures with a cumulative mean of the 21 previous months over the 1945–2012 calibration period. The new IR2Tmax reconstruction is spatially representative for the Iberian Peninsula and captures the full range of past Iberian Range temperature variability. Reconstructed long-term temperature variations match reasonably well with solar irradiance changes since warm and cold phases correspond with high and low solar activity, respectively. In addition, some annual temperature downturns coincide with volcanic eruptions with a 3-year lag.”

Next comes Portugal. Anna Morozova and Tatiana Barlyaeva analyzed the temperature curve of the past 100 years in Lisbon, Coimbra and Porto. Here they found a weak but statistically well supported signal of the 11-year and 22-year solar cycles on the temperature data. In the study’s main text we read:

Weak but statistically significant (bi-)decadal signals in the temperature series that can be associated with the solar and geomagnetic activity variations were found. These signals are stronger during the spring and autumn seasons. The multiple regression models which include the sunspot numbers or the geomagnetic indices among other regressors have higher prediction quality. The wavelet coherence analysis shows that there are time lags between the temperature variations and the solar activity cycles. These lags are about 1–2 years in case of the 11-yr solar cycle as well as in case of the 22-yr solar magnetic cycle (relatively to the solar polar magnetic field observations). These lags are confirmed by the correlation analysis. The results obtained by these methods as well as comparison to results of other studies allow us to conclude that the found (bi-)decadal temperature variability modes can be associated, at least partly, with the effect of the solar forcing.”

Continuing out into the Atlantic Ocean. The Azores islands play an important role in western European weather. In November 2016 Roy et al. in the Journal of Atmospheric and Solar-Terrestrial Physics looked at the question of whether solar activity could play a role on the well-known Azores highs.

A solar impact on this important weather machine would be of great meaning. And indeed the authors found a significant coupling between the Azores highs and solar activity. The relationship becomes visible foremost when one considers different solar activity characteristic figures, and not only the often used sunspot number. It is becoming increasingly clear that the solar magnetic field plays a just as important role — and brought the needed breakthrough in the case of the Azores.

Time delay effects of 1 to 2 years do have be accounted for. The climate system lags a bit and does not immediately react to every impulse that comes up. Sometimes it takes a little time before the system reacts and adjusts to external factors. What follows is the abstract of the exciting study:

Comparing the influence of sunspot activity and geomagnetic activity on winter surface climate
We compare here the effect of geomagnetic activity (using the aa index) and sunspot activity on surface climate using sea level pressure dataset from Hadley centre during northern winter. Previous studies using the multiple linear regression method have been limited to using sunspots as a solar activity predictor. Sunspots and total solar irradiance indicate a robust positive influence around the Aleutian Low. This is valid up to a lag of one year. However, geomagnetic activity yields a positive NAM pattern at high to polar latitudes and a positive signal around Azores High pressure region. Interestingly, while there is a positive signal around Azores High for a 2-year lag in sunspots, the strongest signal in this region is found for aa index at 1-year lag. There is also a weak but significant negative signature present around central Pacific for both sunspots and aa index. The combined influence of geomagnetic activity and Quasi Biannual Oscillation (QBO 30 hPa) produces a particularly strong response at mid to polar latitudes, much stronger than the combined influence of sunspots and QBO, which was mostly studied in previous studies so far. This signal is robust and insensitive to the selected time period during the last century. Our results provide a useful way for improving the prediction of winter weather at middle to high latitudes of the northern hemisphere.”

Or with Willis or Leif at WUWT who are both very much against the sun playing any significant role; I think that Leif suggest that it can account for only about 0.1degC.

Whilst I do not like predicting the future, presently it appears that we are in for a period of an inactive sun so perhaps we will have further insight within the next 20 to 30 years. Of course, even if there is some cooling over the next 20 or 30 years, and even if the sun remains quiet during this period, one can never rule out mere coincidence. Such are the problems of climate science.

But of course, should this happen and should CO2 emissions rise unabated then the case for CO2 being a significant driver becomes ever more difficult.

Or with Willis or Leif at WUWT who are both very much against the sun playing any significant role; I think that Leif suggest that it can account for only about 0.1degC.

Whilst I do not like predicting the future, presently it appears that we are in for a period of an inactive sun so perhaps we will have further insight within the next 20 to 30 years. Of course, even if there is some cooling over the next 20 or 30 years, and even if the sun remains quiet during this period, one can never rule out mere coincidence. Such are the problems of climate science.

But of course, should this happen and should CO2 emissions rise unabated then the case for CO2 being a significant driver becomes ever more difficult.